The invention relates to a device for concentrating the components contained in a flowing medium, which device is provided with inlet and outlet ends for an axial flow, as well as with a porous sorbent bed arranged therebetween, in which bed components can be absorbed or adsorbed from the medium flow conducted through the bed, said bed being electroconductive, so that the components can be desorbed to a washing flow conducted through the bed by heating the bed with an axially oriented electric current. In addition, the invention relates to equipment for analyzing components contained in a flowing medium, said equipment comprising, apart from a sorbent bed absorbing or adsorbing components, an analyzer that is in flowing communication with the bed, for defining the components desorbed from the bed, as well as an analyzing method for applying the described analyzing equipment.
The publication WO 96/09887 describes an adsorber that is meant for cleaning a flowing medium of impurities contained therein, and for separating different impurities from each other. The device comprises a sorbent bed made of activated carbon, through which a flow is arranged to pass, as well as electrodes provided at the sides of the bed for heating the bed by electric current that is conducted transversally therethrough. According to said publication, the sorbent bed temperature is raised stepwise, so that the components that are adsorbed in the bed and desorbed therefrom at different temperatures are separated from each other as the bed is regenerated. Desorption can take place into an inert gas flow or, as an alternative, the desorbed components can be removed from the bed by vacuum ventilation.
Similar equipment is introduced in the publication WO 96/09104, where the sorbent bed is used for separating components contained in a flow by heating the bed already in the adsorption step, so that the more strongly adsorbed component is maintained in the bed, whereas the less strongly adsorbed component remains in the flow penetrating the bed. Thereafter the bed is regenerated by heating it more, so that said adsorbed component is desorbed and can be removed to a cleaning flow composed of an inert gas, such as nitrogen, or extracted by vacuum ventilation. In this publication the sorbent bed is encased in a non-conductive sheath, made for instance of ceramic material, and in the adsorption and desorption steps of the bed, the heating electric current is conducted through the bed in the direction of the gas flows. As an example, the publication mentions the separation of trichloroethylene impurities from a humid air flow.
The publication WO 96/09886 likewise describes a sorbent bed made of activated carbon and adsorbing components from a flow, through which bed the flow passes in the vertical direction. For regenerating the bed, the heating, component-desorbing electric current is conducted through the bed in the horizontal direction. Because the bed material is, owing to the effect of gravity, compacted in the lower part of the bed, and thus the electric resistance of the material in the lower part of the bed is lower than in the upper part, the heating in a uniformly wide bed takes place unevenly. As a solution for this problem, the bed described in the publication is made to be downwardly expanding in the vertical direction, cf. FIG. 6 of said publication, in which case the resistance in the lower part of the bed increases.
The publication U.S. Pat. No. 7,299,711 describes an arrangement for adsorbing contaminants from a flow and for desorbing them, which arrangement functionally corresponds to the one introduced in the above described publications, but which comprises, instead of a sorbent bed made of activated carbon, an adsorbing and desorbing metal mesh or felt-like mat made of metal wire. To said mesh or mat, there is connected an analyzer for detecting components that are separated from the bed by selective desorption.
In the publication U.S. Pat. No. 4,019,021, there is described an electric heater for a liquid or gas flow, where the flow is conducted through a bed made of electroconductive material and arranged inside a tubular structure. The tubular structure and the bed contained therein are narrowed in the flowing direction in order to heat the bed material more strongly at the final end of the bed. By this arrangement, there is achieved a progressive heating of the flow, at the same time as the flow rate is increased owing to the narrowing shape of the tube, and the resident time of the flow is shortened at the final end of the bed. The purpose is to protect the heat-sensitive components contained in the flow from being broken up. The publication does not mention absorption or desorption of the components.
If a heating electric current is conducted through the sorbent bed axially, i.e. in parallel with the medium flow, from which components are absorbed or adsorbed, and/or in parallel with the washing flow, into which components are desorbed, as must be done when placing a sorbent bed in an electrically insulating tube or when encasing it in an electrically insulating sheath, the heating power in a cylindrical bed is constant along the whole length of the bed. However, when a washing flow is started, its bed-cooling effect at the first end of the bed is stronger than at the final end, and as a consequence, the final end of the bed is heated more than the first end. This in turn weakens the sharpness of the resolution of components in a bed, where the volume and heating power of the electric current conducted therethrough is gradually increased. From the hotter final end of the bed, there tend to be desorbed and washed away such components that at the cooler first end of the bed still remain attached to the bed material.